PVD coated cutting tools are well known in the art. PVD coatings usually have a high hardness and are desired for its high wear resistance, e.g. high resistance against flank and crater wear. However, such coatings can be brittle which can cause problems, such as flaking, when deposited onto substrates having a high toughness and also onto substrates having sharp geometries.
Cemented carbide substrates having a high toughness are typically cemented carbide having a high cobalt content. An increased cobalt content increases the toughness of the cemented carbide but also decreases the hardness. By applying a more fine-grained substrate, the hardness of the cemented carbide can be increased.
Fine grained cemented carbide substrates with PVD coatings are known in the art.
EP 1 803 830 A1 discloses a cemented carbide having a WC mean particle diameter less than 0.3 μm. This cemented carbide is particularly suitable for micro-drills used for printed circuit boards. EP 1 803 830 A1 does not disclose a coating.
WO 2010/002344 A1 discloses a cutting tool insert for turning of steels comprising a substrate and a coating where the substrate comprises WC, 8.5-11.5 wt-% Co, 0.8-1.2 wt-% Cr and a coercivity of 19-23 kA/m and a coating comprising an inner (ALTON-layer and a (Al,Cr)O-layer.
However, cobalt contents above 12 wt % has still, in many applications, been considered to be too high to achieve a substrate having a high toughness but with enough hardness to be coated with a PVD-coating.
It is an object of the present invention to obtain a coated cutting tool having a hard coating deposited onto a substrate having a high toughness.
It is yet another object of the present invention to obtain a coated cutting tool that will increase the edge line toughness.
It has been found that the objectives above can be met by combining a PVD coating with a fine grained cemented carbide substrate having a cobalt content as high as 12.5-17 wt %, a Cr content such that the Cr/Co weight ratio is 0.05-0.15 and a Ti content of between 50 to 300 ppm by weight.